This invention relates to a digital/analog converter and more particularly to a two-dimensional symmetric thermometer matrix decoder of digital/analog converter designed to reduce an integral non-linearity error due to current gradient of a current source by making a selected current source two-dimensional and symmetrical.
A conventional digital/analog converter, as shown in FIG. 1, is run using an unweighted thermometer method where the current is gained by activating current sources I1-In capable of flowing the current. The digital/analog converter that is run with an un-weighted thermometer method outputs Io=I1+I2+ . . . In=nI . . . (1). Wherein, n is an integer.
However, on a real device, it is impossible to make current sources that are exactly the same. Thus, as shown in FIG. 2, the current value of each current source differs from each other causing an integral non-linearity error whose actual value is different from its theoretical value as depicted in FIG. 3. In a digital/analog converter, this error must be smaller than a half the amount of the current flowing when one current source is being activated. However, the value of an integral non-linearity error increases as the number of the current sources becomes larger, thereby restricting the increase in the number of digital bits used in a digital/analog converter.